A portion of the power generated by an aviation turbine engine is used for supplying various members of the turbine engine but also of the aircraft whose turbine engine participates in the propulsion.
A portion of this power is currently taken off at the high-pressure compressor, whose compressed air is used particularly for pressurizing and air conditioning the aircraft cabin, or else deicing. Another portion of this power is taken off mechanically from the shaft of the high-pressure (HP) body of the turbine engine, in order to drive the input shaft of an accessory gearbox. This input shaft is rotated by a transmission shaft extending in a structural arm of the casing and itself driven by a gear fixedly attached to the HP shaft.
The accessory gearbox (AGB), well known to those skilled in the art, comprises various machines, or accessories, for example an electric generator, a starter, an alternator, hydraulic, fuel or oil pumps, etc. These various accessories are mechanically driven by the power taken off from the HP shaft as has just been seen.
The current trend aims to increase the portion of the mechanical power offtake that is converted into electric power because of the increasing role of electric means that are considered to be more flexible to use on the aircraft.
However, too high a mechanical power offtake has a negative effect on the operation of the HP body, because it is capable of causing pumping of the HP compressor, in particular when the engine operates at low speed. This effect is all the more problematic when the demand for power is just as great, if not greater, at idle speeds as at cruising or “full throttle” speeds: the offtake from the HP body, as a proportion of the total power, is then very great and the risk of pumping very high.